Cholesteric liquid crystal (CLC) reflective technology is a technology which utilizes several bistable liquid crystal monomers having similar molecular structures to cholesterol, to reflect colorful light according to the molecular torsion state. Macromolecular Liquid Crystalline Films (MLCF), which can be created from adding a polymer containing an acrylate group to the CLC structure further curing by UV, have special optical properties to be applicable to various display devices. The CLC molecule has a spiral structure which can selectively reflect wavelength of the MLCF. The bands of the reflected wavelength are related to the pitches of the CLC molecule, which can be represented by the following equation (1).λ=np  (1),
wherein λ is a reflective wavelength, p is a pitch of the CLC molecule, and n is a value of the dielectric anisotropy of the cholesteric phase.
Pitches of the CLC molecule can be changed in different ways to control bands of the reflection of the MLCF to create red, green, or blue light. Conventionally known photo-crosslinkable compound having a chiral center can be added into room temperature nematic liquid crystal (NLC) or CLC to get a wider reflection band and a higher reflective intensity of the liquid crystal by controlling the concentrations thereof. When the concentrations are increased, the pitches of the CLC molecule are also increased. Then, a polymer is added into the CLC, and after photocrosslinking reaction, the polymer will have chain reactions to wrap up the CLC molecules, making the CLC change from a liquid state to a solid state. Thus, adding a photo-crosslinkable compound can control the color and color saturation of the reflection of the room temperature NLC or CLC.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a relationship between wavelength and reflectance of the reflection of CLC molecules. The CLC molecules form a macromolecule membrane after polyreaction. The wavelength of the reflection of the CLC molecules can be adjusted by adding various concentrations of the chiral molecules. The CLC molecules which are added different amounts of chiral molecules have different helical twisting power (HTP) to vary due to added amounts, thus reflection wavelength can be fallen blue, green, or red band.
Currently known optically active compounds have low HTP, which cause poor compatibility between the optically active compounds and the CLC, and do not have a liquid crystalline phase. In addition, in order to get the desired reflecting property of the CLC, there needs to be added more optically active compounds.
Thus, there is a need for an improved optically active compound to overcome the above-mentioned difficulties.